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<div class="title">RunQueue.h</div>  </div>
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<div class="fragment"><div class="line"><a name="l00001"></a><span class="lineno">    1</span>&#160;<span class="comment">// This file is part of Eigen, a lightweight C++ template library</span></div>
<div class="line"><a name="l00002"></a><span class="lineno">    2</span>&#160;<span class="comment">// for linear algebra.</span></div>
<div class="line"><a name="l00003"></a><span class="lineno">    3</span>&#160;<span class="comment">//</span></div>
<div class="line"><a name="l00004"></a><span class="lineno">    4</span>&#160;<span class="comment">// Copyright (C) 2016 Dmitry Vyukov &lt;dvyukov@google.com&gt;</span></div>
<div class="line"><a name="l00005"></a><span class="lineno">    5</span>&#160;<span class="comment">//</span></div>
<div class="line"><a name="l00006"></a><span class="lineno">    6</span>&#160;<span class="comment">// This Source Code Form is subject to the terms of the Mozilla</span></div>
<div class="line"><a name="l00007"></a><span class="lineno">    7</span>&#160;<span class="comment">// Public License v. 2.0. If a copy of the MPL was not distributed</span></div>
<div class="line"><a name="l00008"></a><span class="lineno">    8</span>&#160;<span class="comment">// with this file, You can obtain one at http://mozilla.org/MPL/2.0/.</span></div>
<div class="line"><a name="l00009"></a><span class="lineno">    9</span>&#160; </div>
<div class="line"><a name="l00010"></a><span class="lineno">   10</span>&#160;<span class="preprocessor">#ifndef EIGEN_CXX11_THREADPOOL_RUNQUEUE_H</span></div>
<div class="line"><a name="l00011"></a><span class="lineno">   11</span>&#160;<span class="preprocessor">#define EIGEN_CXX11_THREADPOOL_RUNQUEUE_H</span></div>
<div class="line"><a name="l00012"></a><span class="lineno">   12</span>&#160; </div>
<div class="line"><a name="l00013"></a><span class="lineno">   13</span>&#160;<span class="preprocessor">#include &quot;./InternalHeaderCheck.h&quot;</span></div>
<div class="line"><a name="l00014"></a><span class="lineno">   14</span>&#160; </div>
<div class="line"><a name="l00015"></a><span class="lineno">   15</span>&#160;<span class="keyword">namespace </span><a class="code" href="namespaceEigen.html">Eigen</a> {</div>
<div class="line"><a name="l00016"></a><span class="lineno">   16</span>&#160; </div>
<div class="line"><a name="l00017"></a><span class="lineno">   17</span>&#160;<span class="comment">// RunQueue is a fixed-size, partially non-blocking deque or Work items.</span></div>
<div class="line"><a name="l00018"></a><span class="lineno">   18</span>&#160;<span class="comment">// Operations on front of the queue must be done by a single thread (owner),</span></div>
<div class="line"><a name="l00019"></a><span class="lineno">   19</span>&#160;<span class="comment">// operations on back of the queue can be done by multiple threads concurrently.</span></div>
<div class="line"><a name="l00020"></a><span class="lineno">   20</span>&#160;<span class="comment">//</span></div>
<div class="line"><a name="l00021"></a><span class="lineno">   21</span>&#160;<span class="comment">// Algorithm outline:</span></div>
<div class="line"><a name="l00022"></a><span class="lineno">   22</span>&#160;<span class="comment">// All remote threads operating on the queue back are serialized by a mutex.</span></div>
<div class="line"><a name="l00023"></a><span class="lineno">   23</span>&#160;<span class="comment">// This ensures that at most two threads access state: owner and one remote</span></div>
<div class="line"><a name="l00024"></a><span class="lineno">   24</span>&#160;<span class="comment">// thread (Size aside). The algorithm ensures that the occupied region of the</span></div>
<div class="line"><a name="l00025"></a><span class="lineno">   25</span>&#160;<span class="comment">// underlying array is logically continuous (can wraparound, but no stray</span></div>
<div class="line"><a name="l00026"></a><span class="lineno">   26</span>&#160;<span class="comment">// occupied elements). Owner operates on one end of this region, remote thread</span></div>
<div class="line"><a name="l00027"></a><span class="lineno">   27</span>&#160;<span class="comment">// operates on the other end. Synchronization between these threads</span></div>
<div class="line"><a name="l00028"></a><span class="lineno">   28</span>&#160;<span class="comment">// (potential consumption of the last element and take up of the last empty</span></div>
<div class="line"><a name="l00029"></a><span class="lineno">   29</span>&#160;<span class="comment">// element) happens by means of state variable in each element. States are:</span></div>
<div class="line"><a name="l00030"></a><span class="lineno">   30</span>&#160;<span class="comment">// empty, busy (in process of insertion of removal) and ready. Threads claim</span></div>
<div class="line"><a name="l00031"></a><span class="lineno">   31</span>&#160;<span class="comment">// elements (empty-&gt;busy and ready-&gt;busy transitions) by means of a CAS</span></div>
<div class="line"><a name="l00032"></a><span class="lineno">   32</span>&#160;<span class="comment">// operation. The finishing transition (busy-&gt;empty and busy-&gt;ready) are done</span></div>
<div class="line"><a name="l00033"></a><span class="lineno">   33</span>&#160;<span class="comment">// with plain store as the element is exclusively owned by the current thread.</span></div>
<div class="line"><a name="l00034"></a><span class="lineno">   34</span>&#160;<span class="comment">//</span></div>
<div class="line"><a name="l00035"></a><span class="lineno">   35</span>&#160;<span class="comment">// Note: we could permit only pointers as elements, then we would not need</span></div>
<div class="line"><a name="l00036"></a><span class="lineno">   36</span>&#160;<span class="comment">// separate state variable as null/non-null pointer value would serve as state,</span></div>
<div class="line"><a name="l00037"></a><span class="lineno">   37</span>&#160;<span class="comment">// but that would require malloc/free per operation for large, complex values</span></div>
<div class="line"><a name="l00038"></a><span class="lineno">   38</span>&#160;<span class="comment">// (and this is designed to store std::function&lt;()&gt;).</span></div>
<div class="line"><a name="l00039"></a><span class="lineno">   39</span>&#160;<span class="keyword">template</span> &lt;<span class="keyword">typename</span> Work, <span class="keywordtype">unsigned</span> kSize&gt;</div>
<div class="line"><a name="l00040"></a><span class="lineno">   40</span>&#160;<span class="keyword">class </span>RunQueue {</div>
<div class="line"><a name="l00041"></a><span class="lineno">   41</span>&#160; <span class="keyword">public</span>:</div>
<div class="line"><a name="l00042"></a><span class="lineno">   42</span>&#160;  RunQueue() : front_(0), back_(0) {</div>
<div class="line"><a name="l00043"></a><span class="lineno">   43</span>&#160;    <span class="comment">// require power-of-two for fast masking</span></div>
<div class="line"><a name="l00044"></a><span class="lineno">   44</span>&#160;    eigen_plain_assert((kSize &amp; (kSize - 1)) == 0);</div>
<div class="line"><a name="l00045"></a><span class="lineno">   45</span>&#160;    eigen_plain_assert(kSize &gt; 2);            <span class="comment">// why would you do this?</span></div>
<div class="line"><a name="l00046"></a><span class="lineno">   46</span>&#160;    eigen_plain_assert(kSize &lt;= (64 &lt;&lt; 10));  <span class="comment">// leave enough space for counter</span></div>
<div class="line"><a name="l00047"></a><span class="lineno">   47</span>&#160;    <span class="keywordflow">for</span> (<span class="keywordtype">unsigned</span> i = 0; i &lt; kSize; i++)</div>
<div class="line"><a name="l00048"></a><span class="lineno">   48</span>&#160;      array_[i].state.store(kEmpty, std::memory_order_relaxed);</div>
<div class="line"><a name="l00049"></a><span class="lineno">   49</span>&#160;  }</div>
<div class="line"><a name="l00050"></a><span class="lineno">   50</span>&#160; </div>
<div class="line"><a name="l00051"></a><span class="lineno">   51</span>&#160;  ~RunQueue() { eigen_plain_assert(Size() == 0); }</div>
<div class="line"><a name="l00052"></a><span class="lineno">   52</span>&#160; </div>
<div class="line"><a name="l00053"></a><span class="lineno">   53</span>&#160;  <span class="comment">// PushFront inserts w at the beginning of the queue.</span></div>
<div class="line"><a name="l00054"></a><span class="lineno">   54</span>&#160;  <span class="comment">// If queue is full returns w, otherwise returns default-constructed Work.</span></div>
<div class="line"><a name="l00055"></a><span class="lineno">   55</span>&#160;  Work PushFront(Work w) {</div>
<div class="line"><a name="l00056"></a><span class="lineno">   56</span>&#160;    <span class="keywordtype">unsigned</span> front = front_.load(std::memory_order_relaxed);</div>
<div class="line"><a name="l00057"></a><span class="lineno">   57</span>&#160;    Elem* e = &amp;array_[front &amp; kMask];</div>
<div class="line"><a name="l00058"></a><span class="lineno">   58</span>&#160;    uint8_t s = e-&gt;state.load(std::memory_order_relaxed);</div>
<div class="line"><a name="l00059"></a><span class="lineno">   59</span>&#160;    <span class="keywordflow">if</span> (s != kEmpty ||</div>
<div class="line"><a name="l00060"></a><span class="lineno">   60</span>&#160;        !e-&gt;state.compare_exchange_strong(s, kBusy, std::memory_order_acquire))</div>
<div class="line"><a name="l00061"></a><span class="lineno">   61</span>&#160;      <span class="keywordflow">return</span> w;</div>
<div class="line"><a name="l00062"></a><span class="lineno">   62</span>&#160;    front_.store(front + 1 + (kSize &lt;&lt; 1), std::memory_order_relaxed);</div>
<div class="line"><a name="l00063"></a><span class="lineno">   63</span>&#160;    e-&gt;w = std::move(w);</div>
<div class="line"><a name="l00064"></a><span class="lineno">   64</span>&#160;    e-&gt;state.store(kReady, std::memory_order_release);</div>
<div class="line"><a name="l00065"></a><span class="lineno">   65</span>&#160;    <span class="keywordflow">return</span> Work();</div>
<div class="line"><a name="l00066"></a><span class="lineno">   66</span>&#160;  }</div>
<div class="line"><a name="l00067"></a><span class="lineno">   67</span>&#160; </div>
<div class="line"><a name="l00068"></a><span class="lineno">   68</span>&#160;  <span class="comment">// PopFront removes and returns the first element in the queue.</span></div>
<div class="line"><a name="l00069"></a><span class="lineno">   69</span>&#160;  <span class="comment">// If the queue was empty returns default-constructed Work.</span></div>
<div class="line"><a name="l00070"></a><span class="lineno">   70</span>&#160;  Work PopFront() {</div>
<div class="line"><a name="l00071"></a><span class="lineno">   71</span>&#160;    <span class="keywordtype">unsigned</span> front = front_.load(std::memory_order_relaxed);</div>
<div class="line"><a name="l00072"></a><span class="lineno">   72</span>&#160;    Elem* e = &amp;array_[(front - 1) &amp; kMask];</div>
<div class="line"><a name="l00073"></a><span class="lineno">   73</span>&#160;    uint8_t s = e-&gt;state.load(std::memory_order_relaxed);</div>
<div class="line"><a name="l00074"></a><span class="lineno">   74</span>&#160;    <span class="keywordflow">if</span> (s != kReady ||</div>
<div class="line"><a name="l00075"></a><span class="lineno">   75</span>&#160;        !e-&gt;state.compare_exchange_strong(s, kBusy, std::memory_order_acquire))</div>
<div class="line"><a name="l00076"></a><span class="lineno">   76</span>&#160;      <span class="keywordflow">return</span> Work();</div>
<div class="line"><a name="l00077"></a><span class="lineno">   77</span>&#160;    Work w = std::move(e-&gt;w);</div>
<div class="line"><a name="l00078"></a><span class="lineno">   78</span>&#160;    e-&gt;state.store(kEmpty, std::memory_order_release);</div>
<div class="line"><a name="l00079"></a><span class="lineno">   79</span>&#160;    front = ((front - 1) &amp; kMask2) | (front &amp; ~kMask2);</div>
<div class="line"><a name="l00080"></a><span class="lineno">   80</span>&#160;    front_.store(front, std::memory_order_relaxed);</div>
<div class="line"><a name="l00081"></a><span class="lineno">   81</span>&#160;    <span class="keywordflow">return</span> w;</div>
<div class="line"><a name="l00082"></a><span class="lineno">   82</span>&#160;  }</div>
<div class="line"><a name="l00083"></a><span class="lineno">   83</span>&#160; </div>
<div class="line"><a name="l00084"></a><span class="lineno">   84</span>&#160;  <span class="comment">// PushBack adds w at the end of the queue.</span></div>
<div class="line"><a name="l00085"></a><span class="lineno">   85</span>&#160;  <span class="comment">// If queue is full returns w, otherwise returns default-constructed Work.</span></div>
<div class="line"><a name="l00086"></a><span class="lineno">   86</span>&#160;  Work PushBack(Work w) {</div>
<div class="line"><a name="l00087"></a><span class="lineno">   87</span>&#160;    std::unique_lock&lt;std::mutex&gt; lock(mutex_);</div>
<div class="line"><a name="l00088"></a><span class="lineno">   88</span>&#160;    <span class="keywordtype">unsigned</span> back = back_.load(std::memory_order_relaxed);</div>
<div class="line"><a name="l00089"></a><span class="lineno">   89</span>&#160;    Elem* e = &amp;array_[(back - 1) &amp; kMask];</div>
<div class="line"><a name="l00090"></a><span class="lineno">   90</span>&#160;    uint8_t s = e-&gt;state.load(std::memory_order_relaxed);</div>
<div class="line"><a name="l00091"></a><span class="lineno">   91</span>&#160;    <span class="keywordflow">if</span> (s != kEmpty ||</div>
<div class="line"><a name="l00092"></a><span class="lineno">   92</span>&#160;        !e-&gt;state.compare_exchange_strong(s, kBusy, std::memory_order_acquire))</div>
<div class="line"><a name="l00093"></a><span class="lineno">   93</span>&#160;      <span class="keywordflow">return</span> w;</div>
<div class="line"><a name="l00094"></a><span class="lineno">   94</span>&#160;    back = ((back - 1) &amp; kMask2) | (back &amp; ~kMask2);</div>
<div class="line"><a name="l00095"></a><span class="lineno">   95</span>&#160;    back_.store(back, std::memory_order_relaxed);</div>
<div class="line"><a name="l00096"></a><span class="lineno">   96</span>&#160;    e-&gt;w = std::move(w);</div>
<div class="line"><a name="l00097"></a><span class="lineno">   97</span>&#160;    e-&gt;state.store(kReady, std::memory_order_release);</div>
<div class="line"><a name="l00098"></a><span class="lineno">   98</span>&#160;    <span class="keywordflow">return</span> Work();</div>
<div class="line"><a name="l00099"></a><span class="lineno">   99</span>&#160;  }</div>
<div class="line"><a name="l00100"></a><span class="lineno">  100</span>&#160; </div>
<div class="line"><a name="l00101"></a><span class="lineno">  101</span>&#160;  <span class="comment">// PopBack removes and returns the last elements in the queue.</span></div>
<div class="line"><a name="l00102"></a><span class="lineno">  102</span>&#160;  Work PopBack() {</div>
<div class="line"><a name="l00103"></a><span class="lineno">  103</span>&#160;    <span class="keywordflow">if</span> (Empty()) <span class="keywordflow">return</span> Work();</div>
<div class="line"><a name="l00104"></a><span class="lineno">  104</span>&#160;    std::unique_lock&lt;std::mutex&gt; lock(mutex_);</div>
<div class="line"><a name="l00105"></a><span class="lineno">  105</span>&#160;    <span class="keywordtype">unsigned</span> back = back_.load(std::memory_order_relaxed);</div>
<div class="line"><a name="l00106"></a><span class="lineno">  106</span>&#160;    Elem* e = &amp;array_[back &amp; kMask];</div>
<div class="line"><a name="l00107"></a><span class="lineno">  107</span>&#160;    uint8_t s = e-&gt;state.load(std::memory_order_relaxed);</div>
<div class="line"><a name="l00108"></a><span class="lineno">  108</span>&#160;    <span class="keywordflow">if</span> (s != kReady ||</div>
<div class="line"><a name="l00109"></a><span class="lineno">  109</span>&#160;        !e-&gt;state.compare_exchange_strong(s, kBusy, std::memory_order_acquire))</div>
<div class="line"><a name="l00110"></a><span class="lineno">  110</span>&#160;      <span class="keywordflow">return</span> Work();</div>
<div class="line"><a name="l00111"></a><span class="lineno">  111</span>&#160;    Work w = std::move(e-&gt;w);</div>
<div class="line"><a name="l00112"></a><span class="lineno">  112</span>&#160;    e-&gt;state.store(kEmpty, std::memory_order_release);</div>
<div class="line"><a name="l00113"></a><span class="lineno">  113</span>&#160;    back_.store(back + 1 + (kSize &lt;&lt; 1), std::memory_order_relaxed);</div>
<div class="line"><a name="l00114"></a><span class="lineno">  114</span>&#160;    <span class="keywordflow">return</span> w;</div>
<div class="line"><a name="l00115"></a><span class="lineno">  115</span>&#160;  }</div>
<div class="line"><a name="l00116"></a><span class="lineno">  116</span>&#160; </div>
<div class="line"><a name="l00117"></a><span class="lineno">  117</span>&#160;  <span class="comment">// PopBackHalf removes and returns half last elements in the queue.</span></div>
<div class="line"><a name="l00118"></a><span class="lineno">  118</span>&#160;  <span class="comment">// Returns number of elements removed.</span></div>
<div class="line"><a name="l00119"></a><span class="lineno">  119</span>&#160;  <span class="keywordtype">unsigned</span> PopBackHalf(std::vector&lt;Work&gt;* result) {</div>
<div class="line"><a name="l00120"></a><span class="lineno">  120</span>&#160;    <span class="keywordflow">if</span> (Empty()) <span class="keywordflow">return</span> 0;</div>
<div class="line"><a name="l00121"></a><span class="lineno">  121</span>&#160;    std::unique_lock&lt;std::mutex&gt; lock(mutex_);</div>
<div class="line"><a name="l00122"></a><span class="lineno">  122</span>&#160;    <span class="keywordtype">unsigned</span> back = back_.load(std::memory_order_relaxed);</div>
<div class="line"><a name="l00123"></a><span class="lineno">  123</span>&#160;    <span class="keywordtype">unsigned</span> size = Size();</div>
<div class="line"><a name="l00124"></a><span class="lineno">  124</span>&#160;    <span class="keywordtype">unsigned</span> mid = back;</div>
<div class="line"><a name="l00125"></a><span class="lineno">  125</span>&#160;    <span class="keywordflow">if</span> (size &gt; 1) mid = back + (size - 1) / 2;</div>
<div class="line"><a name="l00126"></a><span class="lineno">  126</span>&#160;    <span class="keywordtype">unsigned</span> n = 0;</div>
<div class="line"><a name="l00127"></a><span class="lineno">  127</span>&#160;    <span class="keywordtype">unsigned</span> start = 0;</div>
<div class="line"><a name="l00128"></a><span class="lineno">  128</span>&#160;    <span class="keywordflow">for</span> (; <span class="keyword">static_cast&lt;</span><span class="keywordtype">int</span><span class="keyword">&gt;</span>(mid - back) &gt;= 0; mid--) {</div>
<div class="line"><a name="l00129"></a><span class="lineno">  129</span>&#160;      Elem* e = &amp;array_[mid &amp; kMask];</div>
<div class="line"><a name="l00130"></a><span class="lineno">  130</span>&#160;      uint8_t s = e-&gt;state.load(std::memory_order_relaxed);</div>
<div class="line"><a name="l00131"></a><span class="lineno">  131</span>&#160;      <span class="keywordflow">if</span> (n == 0) {</div>
<div class="line"><a name="l00132"></a><span class="lineno">  132</span>&#160;        <span class="keywordflow">if</span> (s != kReady || !e-&gt;state.compare_exchange_strong(</div>
<div class="line"><a name="l00133"></a><span class="lineno">  133</span>&#160;                               s, kBusy, std::memory_order_acquire))</div>
<div class="line"><a name="l00134"></a><span class="lineno">  134</span>&#160;          <span class="keywordflow">continue</span>;</div>
<div class="line"><a name="l00135"></a><span class="lineno">  135</span>&#160;        start = mid;</div>
<div class="line"><a name="l00136"></a><span class="lineno">  136</span>&#160;      } <span class="keywordflow">else</span> {</div>
<div class="line"><a name="l00137"></a><span class="lineno">  137</span>&#160;        <span class="comment">// Note: no need to store temporal kBusy, we exclusively own these</span></div>
<div class="line"><a name="l00138"></a><span class="lineno">  138</span>&#160;        <span class="comment">// elements.</span></div>
<div class="line"><a name="l00139"></a><span class="lineno">  139</span>&#160;        eigen_plain_assert(s == kReady);</div>
<div class="line"><a name="l00140"></a><span class="lineno">  140</span>&#160;      }</div>
<div class="line"><a name="l00141"></a><span class="lineno">  141</span>&#160;      result-&gt;push_back(std::move(e-&gt;w));</div>
<div class="line"><a name="l00142"></a><span class="lineno">  142</span>&#160;      e-&gt;state.store(kEmpty, std::memory_order_release);</div>
<div class="line"><a name="l00143"></a><span class="lineno">  143</span>&#160;      n++;</div>
<div class="line"><a name="l00144"></a><span class="lineno">  144</span>&#160;    }</div>
<div class="line"><a name="l00145"></a><span class="lineno">  145</span>&#160;    <span class="keywordflow">if</span> (n != 0)</div>
<div class="line"><a name="l00146"></a><span class="lineno">  146</span>&#160;      back_.store(start + 1 + (kSize &lt;&lt; 1), std::memory_order_relaxed);</div>
<div class="line"><a name="l00147"></a><span class="lineno">  147</span>&#160;    <span class="keywordflow">return</span> n;</div>
<div class="line"><a name="l00148"></a><span class="lineno">  148</span>&#160;  }</div>
<div class="line"><a name="l00149"></a><span class="lineno">  149</span>&#160; </div>
<div class="line"><a name="l00150"></a><span class="lineno">  150</span>&#160;  <span class="comment">// Size returns current queue size.</span></div>
<div class="line"><a name="l00151"></a><span class="lineno">  151</span>&#160;  <span class="comment">// Can be called by any thread at any time.</span></div>
<div class="line"><a name="l00152"></a><span class="lineno">  152</span>&#160;  <span class="keywordtype">unsigned</span> Size()<span class="keyword"> const </span>{ <span class="keywordflow">return</span> SizeOrNotEmpty&lt;true&gt;(); }</div>
<div class="line"><a name="l00153"></a><span class="lineno">  153</span>&#160; </div>
<div class="line"><a name="l00154"></a><span class="lineno">  154</span>&#160;  <span class="comment">// Empty tests whether container is empty.</span></div>
<div class="line"><a name="l00155"></a><span class="lineno">  155</span>&#160;  <span class="comment">// Can be called by any thread at any time.</span></div>
<div class="line"><a name="l00156"></a><span class="lineno">  156</span>&#160;  <span class="keywordtype">bool</span> Empty()<span class="keyword"> const </span>{ <span class="keywordflow">return</span> SizeOrNotEmpty&lt;false&gt;() == 0; }</div>
<div class="line"><a name="l00157"></a><span class="lineno">  157</span>&#160; </div>
<div class="line"><a name="l00158"></a><span class="lineno">  158</span>&#160;  <span class="comment">// Delete all the elements from the queue.</span></div>
<div class="line"><a name="l00159"></a><span class="lineno">  159</span>&#160;  <span class="keywordtype">void</span> Flush() {</div>
<div class="line"><a name="l00160"></a><span class="lineno">  160</span>&#160;    <span class="keywordflow">while</span> (!Empty()) {</div>
<div class="line"><a name="l00161"></a><span class="lineno">  161</span>&#160;      PopFront();</div>
<div class="line"><a name="l00162"></a><span class="lineno">  162</span>&#160;    }</div>
<div class="line"><a name="l00163"></a><span class="lineno">  163</span>&#160;  }</div>
<div class="line"><a name="l00164"></a><span class="lineno">  164</span>&#160; </div>
<div class="line"><a name="l00165"></a><span class="lineno">  165</span>&#160; <span class="keyword">private</span>:</div>
<div class="line"><a name="l00166"></a><span class="lineno">  166</span>&#160;  <span class="keyword">static</span> <span class="keyword">const</span> <span class="keywordtype">unsigned</span> kMask = kSize - 1;</div>
<div class="line"><a name="l00167"></a><span class="lineno">  167</span>&#160;  <span class="keyword">static</span> <span class="keyword">const</span> <span class="keywordtype">unsigned</span> kMask2 = (kSize &lt;&lt; 1) - 1;</div>
<div class="line"><a name="l00168"></a><span class="lineno">  168</span>&#160;  <span class="keyword">struct </span>Elem {</div>
<div class="line"><a name="l00169"></a><span class="lineno">  169</span>&#160;    std::atomic&lt;uint8_t&gt; state;</div>
<div class="line"><a name="l00170"></a><span class="lineno">  170</span>&#160;    Work w;</div>
<div class="line"><a name="l00171"></a><span class="lineno">  171</span>&#160;  };</div>
<div class="line"><a name="l00172"></a><span class="lineno">  172</span>&#160;  <span class="keyword">enum</span> {</div>
<div class="line"><a name="l00173"></a><span class="lineno">  173</span>&#160;    kEmpty,</div>
<div class="line"><a name="l00174"></a><span class="lineno">  174</span>&#160;    kBusy,</div>
<div class="line"><a name="l00175"></a><span class="lineno">  175</span>&#160;    kReady,</div>
<div class="line"><a name="l00176"></a><span class="lineno">  176</span>&#160;  };</div>
<div class="line"><a name="l00177"></a><span class="lineno">  177</span>&#160;  std::mutex mutex_;</div>
<div class="line"><a name="l00178"></a><span class="lineno">  178</span>&#160;  <span class="comment">// Low log(kSize) + 1 bits in front_ and back_ contain rolling index of</span></div>
<div class="line"><a name="l00179"></a><span class="lineno">  179</span>&#160;  <span class="comment">// front/back, respectively. The remaining bits contain modification counters</span></div>
<div class="line"><a name="l00180"></a><span class="lineno">  180</span>&#160;  <span class="comment">// that are incremented on Push operations. This allows us to (1) distinguish</span></div>
<div class="line"><a name="l00181"></a><span class="lineno">  181</span>&#160;  <span class="comment">// between empty and full conditions (if we would use log(kSize) bits for</span></div>
<div class="line"><a name="l00182"></a><span class="lineno">  182</span>&#160;  <span class="comment">// position, these conditions would be indistinguishable); (2) obtain</span></div>
<div class="line"><a name="l00183"></a><span class="lineno">  183</span>&#160;  <span class="comment">// consistent snapshot of front_/back_ for Size operation using the</span></div>
<div class="line"><a name="l00184"></a><span class="lineno">  184</span>&#160;  <span class="comment">// modification counters.</span></div>
<div class="line"><a name="l00185"></a><span class="lineno">  185</span>&#160;  std::atomic&lt;unsigned&gt; front_;</div>
<div class="line"><a name="l00186"></a><span class="lineno">  186</span>&#160;  std::atomic&lt;unsigned&gt; back_;</div>
<div class="line"><a name="l00187"></a><span class="lineno">  187</span>&#160;  Elem array_[kSize];</div>
<div class="line"><a name="l00188"></a><span class="lineno">  188</span>&#160; </div>
<div class="line"><a name="l00189"></a><span class="lineno">  189</span>&#160;  <span class="comment">// SizeOrNotEmpty returns current queue size; if NeedSizeEstimate is false,</span></div>
<div class="line"><a name="l00190"></a><span class="lineno">  190</span>&#160;  <span class="comment">// only whether the size is 0 is guaranteed to be correct.</span></div>
<div class="line"><a name="l00191"></a><span class="lineno">  191</span>&#160;  <span class="comment">// Can be called by any thread at any time.</span></div>
<div class="line"><a name="l00192"></a><span class="lineno">  192</span>&#160;  <span class="keyword">template</span>&lt;<span class="keywordtype">bool</span> NeedSizeEstimate&gt;</div>
<div class="line"><a name="l00193"></a><span class="lineno">  193</span>&#160;  <span class="keywordtype">unsigned</span> SizeOrNotEmpty()<span class="keyword"> const </span>{</div>
<div class="line"><a name="l00194"></a><span class="lineno">  194</span>&#160;    <span class="comment">// Emptiness plays critical role in thread pool blocking. So we go to great</span></div>
<div class="line"><a name="l00195"></a><span class="lineno">  195</span>&#160;    <span class="comment">// effort to not produce false positives (claim non-empty queue as empty).</span></div>
<div class="line"><a name="l00196"></a><span class="lineno">  196</span>&#160;    <span class="keywordtype">unsigned</span> front = front_.load(std::memory_order_acquire);</div>
<div class="line"><a name="l00197"></a><span class="lineno">  197</span>&#160;    <span class="keywordflow">for</span> (;;) {</div>
<div class="line"><a name="l00198"></a><span class="lineno">  198</span>&#160;      <span class="comment">// Capture a consistent snapshot of front/tail.</span></div>
<div class="line"><a name="l00199"></a><span class="lineno">  199</span>&#160;      <span class="keywordtype">unsigned</span> back = back_.load(std::memory_order_acquire);</div>
<div class="line"><a name="l00200"></a><span class="lineno">  200</span>&#160;      <span class="keywordtype">unsigned</span> front1 = front_.load(std::memory_order_relaxed);</div>
<div class="line"><a name="l00201"></a><span class="lineno">  201</span>&#160;      <span class="keywordflow">if</span> (front != front1) {</div>
<div class="line"><a name="l00202"></a><span class="lineno">  202</span>&#160;        front = front1;</div>
<div class="line"><a name="l00203"></a><span class="lineno">  203</span>&#160;        std::atomic_thread_fence(std::memory_order_acquire);</div>
<div class="line"><a name="l00204"></a><span class="lineno">  204</span>&#160;        <span class="keywordflow">continue</span>;</div>
<div class="line"><a name="l00205"></a><span class="lineno">  205</span>&#160;      }</div>
<div class="line"><a name="l00206"></a><span class="lineno">  206</span>&#160;      <span class="keywordflow">if</span> (NeedSizeEstimate) {</div>
<div class="line"><a name="l00207"></a><span class="lineno">  207</span>&#160;        <span class="keywordflow">return</span> CalculateSize(front, back);</div>
<div class="line"><a name="l00208"></a><span class="lineno">  208</span>&#160;      } <span class="keywordflow">else</span> {</div>
<div class="line"><a name="l00209"></a><span class="lineno">  209</span>&#160;        <span class="comment">// This value will be 0 if the queue is empty, and undefined otherwise.</span></div>
<div class="line"><a name="l00210"></a><span class="lineno">  210</span>&#160;        <span class="keywordtype">unsigned</span> maybe_zero = ((front ^ back) &amp; kMask2);</div>
<div class="line"><a name="l00211"></a><span class="lineno">  211</span>&#160;        <span class="comment">// Queue size estimate must agree with maybe zero check on the queue</span></div>
<div class="line"><a name="l00212"></a><span class="lineno">  212</span>&#160;        <span class="comment">// empty/non-empty state.</span></div>
<div class="line"><a name="l00213"></a><span class="lineno">  213</span>&#160;        eigen_assert((CalculateSize(front, back) == 0) == (maybe_zero == 0));</div>
<div class="line"><a name="l00214"></a><span class="lineno">  214</span>&#160;        <span class="keywordflow">return</span> maybe_zero;</div>
<div class="line"><a name="l00215"></a><span class="lineno">  215</span>&#160;      }</div>
<div class="line"><a name="l00216"></a><span class="lineno">  216</span>&#160;    }</div>
<div class="line"><a name="l00217"></a><span class="lineno">  217</span>&#160;  }</div>
<div class="line"><a name="l00218"></a><span class="lineno">  218</span>&#160; </div>
<div class="line"><a name="l00219"></a><span class="lineno">  219</span>&#160;  EIGEN_ALWAYS_INLINE</div>
<div class="line"><a name="l00220"></a><span class="lineno">  220</span>&#160;  <span class="keywordtype">unsigned</span> CalculateSize(<span class="keywordtype">unsigned</span> front, <span class="keywordtype">unsigned</span> back)<span class="keyword"> const </span>{</div>
<div class="line"><a name="l00221"></a><span class="lineno">  221</span>&#160;    <span class="keywordtype">int</span> size = (front &amp; kMask2) - (back &amp; kMask2);</div>
<div class="line"><a name="l00222"></a><span class="lineno">  222</span>&#160;    <span class="comment">// Fix overflow.</span></div>
<div class="line"><a name="l00223"></a><span class="lineno">  223</span>&#160;    <span class="keywordflow">if</span> (size &lt; 0) size += 2 * kSize;</div>
<div class="line"><a name="l00224"></a><span class="lineno">  224</span>&#160;    <span class="comment">// Order of modification in push/pop is crafted to make the queue look</span></div>
<div class="line"><a name="l00225"></a><span class="lineno">  225</span>&#160;    <span class="comment">// larger than it is during concurrent modifications. E.g. push can</span></div>
<div class="line"><a name="l00226"></a><span class="lineno">  226</span>&#160;    <span class="comment">// increment size before the corresponding pop has decremented it.</span></div>
<div class="line"><a name="l00227"></a><span class="lineno">  227</span>&#160;    <span class="comment">// So the computed size can be up to kSize + 1, fix it.</span></div>
<div class="line"><a name="l00228"></a><span class="lineno">  228</span>&#160;    <span class="keywordflow">if</span> (size &gt; <span class="keyword">static_cast&lt;</span><span class="keywordtype">int</span><span class="keyword">&gt;</span>(kSize)) size = kSize;</div>
<div class="line"><a name="l00229"></a><span class="lineno">  229</span>&#160;    <span class="keywordflow">return</span> <span class="keyword">static_cast&lt;</span><span class="keywordtype">unsigned</span><span class="keyword">&gt;</span>(size);</div>
<div class="line"><a name="l00230"></a><span class="lineno">  230</span>&#160;  }</div>
<div class="line"><a name="l00231"></a><span class="lineno">  231</span>&#160; </div>
<div class="line"><a name="l00232"></a><span class="lineno">  232</span>&#160;  RunQueue(<span class="keyword">const</span> RunQueue&amp;) = <span class="keyword">delete</span>;</div>
<div class="line"><a name="l00233"></a><span class="lineno">  233</span>&#160;  <span class="keywordtype">void</span> operator=(<span class="keyword">const</span> RunQueue&amp;) = <span class="keyword">delete</span>;</div>
<div class="line"><a name="l00234"></a><span class="lineno">  234</span>&#160;};</div>
<div class="line"><a name="l00235"></a><span class="lineno">  235</span>&#160; </div>
<div class="line"><a name="l00236"></a><span class="lineno">  236</span>&#160;}  <span class="comment">// namespace Eigen</span></div>
<div class="line"><a name="l00237"></a><span class="lineno">  237</span>&#160; </div>
<div class="line"><a name="l00238"></a><span class="lineno">  238</span>&#160;<span class="preprocessor">#endif  </span><span class="comment">// EIGEN_CXX11_THREADPOOL_RUNQUEUE_H</span></div>
<div class="ttc" id="anamespaceEigen_html"><div class="ttname"><a href="namespaceEigen.html">Eigen</a></div><div class="ttdoc">Namespace containing all symbols from the Eigen library.</div></div>
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